not for the men's shirts though. they were proud that the men's shirts were 100% polyester. They felt the ultra-thin polyester gave them more of an authentic 70's t-shirt look.
but for some reason most of the boys and women's were 100% cotton.
I'm sure at one point they were specifying material for the men's shirts, as well as the 'cut'. I have some 50/50, and some all cotton, but none that are all polyester. The cut made the difference though, as I needed a larger size with the original shirts, and some of the later ones I needed to drop down a size.
Someone mentioned the white shirts - I have just one title on a white shirt, Kentucky Fried Fingers. It's 50/50, and seems to be the same quality as the colored shirts, but it is pretty much see-through, so I only wear it over another shirt. Works great in the winter over a long sleeve thermal shirt, and looks fantastic! I think that was one of their special limited edition titles.